1. Field of the Invention
Embodiments of this invention relate generally to head stack assemblies for suspending and positioning read/write heads over magnetic media of the type generally used for storing digital data, and in particular embodiments to apparatus for non-frictional, head stack-level loading and unloading of read/write heads from the magnetic media, and systems incorporating the same.
2. Description of Related Art
Modern computers require media in which digital data can be quickly stored and retrieved. Magnetizable (hard) layers on disks have proven to be a reliable media for fast and accurate data storage and retrieval. Disk drives that read data from and write data to hard disks have thus become popular components of computer systems. To access memory locations on a hard disk, a read/write head is positioned slightly above the surface of the hard disk while the hard disk rotates beneath the read/write head at an essentially constant velocity. By moving the read/write head radially over the rotating hard disk, all memory locations on the hard disk can be accessed. The read/write head is typically referred to as "flying" head because it includes a slider aerodynamically configured to hover above the surface on an air bearing located between the hard disk and the slider that forms as the hard disk rotates at high speeds. The air bearing supports the read/write head above the disk surface at a height referred to as the "flying height."
In conventional disk drives, multiple hard disks are coupled to and rotate about a spindle, each hard disk presenting two substantially flat surfaces for reading and recording. Typically, multiple rotating hard disks are stacked in a parallel relationship with minimal spacing between them. Accordingly, the read/write heads must be designed to move within the narrow space between adjacent hard disks and fly close to the hard disk surfaces. To achieve this positional capability, the read/write heads in typical disk drives are coupled to the distal end of thin, arm-like structures called head suspension assemblies, which are inserted within the narrow space between adjacent hard disks. These head suspension assemblies are made of materials and thicknesses as to be somewhat flexible and allow a measure of vertical positioning as the read/write heads hover over the surface of the rotating hard disks.
Each head suspension assembly is coupled at its proximal end to a rigid actuator arm that horizontally positions the head suspension assembly and read/write head over the hard disk surface. In conventional disk drives, actuator arms are stacked, forming a multi-arm head stack assembly which moves as a unit under the influence of a voice coil motor to simultaneously position all head suspension assemblies and corresponding read/write heads over the hard disk surfaces.
In conventional disk drive systems, the hard disks rotate at high velocities and read/write heads are positioned over the hard disks with very little air gap separation, and read/write head contact with the hard disks (a head crash) can be catastrophic. Data can be permanently lost, or the read/write heads and hard disks can be damaged such that the entire disk drive system no longer functions. Therefore, modern disk drive systems avoid read/write head contact with the recording areas of hard disks as much as possible. To minimize read/write head contact with the recording areas of hard disks, many disk drives "park" their read/write heads when the disk drive system is powered down or when the hard disks temporarily stop spinning so that the read/write heads rest over parking zones (areas on the hard disks where no data is stored, typically the innermost central region of the disks or an area completely off of the disks). The use of parking zones minimize wear on the recording area of the disks and thus increases the reliability of the disk drive system and the integrity of the stored data.
However, head parking on the innermost region of the hard disk will cause wear on the read/write heads because the read/write heads eventually come into frictional contact with the parking zones as the hard disks stop spinning during a shutdown. This wear will also occur during disk drive startup, as the read/write heads will be in frictional contact with the parking zones until the hard disks have reached a speed sufficient to cause the "flying" of the heads. The problem of wear caused by these frictional start and stop processes is exacerbated by the increasing popularity of portable notebook computers, which require more frequent disk drive starts and stops to minimize power consumption.
Furthermore, the small geometries of modern disk drives makes the design of head parking areas on the innermost regions of hard disks problematic. Head parking areas on hard disks are typically roughened to minimize stiction and prevent the read/write heads from sticking to the disk surfaces. However, the flying height of modern read/write heads is so low that protrusions on surfaces roughened to minimize stiction may exceed the flying height of the read/write heads, making such parking areas effectively unusable for parking purposes.
Because of the problems inherent in head parking on the innermost region of the hard disk, head parking outside the outer diameter of the hard disk has become increasingly prevalent. In this method of head parking, no contact of the read/write heads with the disk surfaces is intended. During startup, the heads are brought in from a parking location off the outer diameter of the hard disk (unparked) and loaded onto the hard disk (placed above the spinning disks). During shutdown, the heads are unloaded (taken off the spinning hard disks) and moved to the parking location. In theory, an air bearing beneath the read/write heads and the spinning hard disks should prevent the read/write heads from touching the hard disks during both the loading and unloading processes. U.S. Pat. No. 5,289,325 (hereinafter the '325 patent) to Morehouse et al., incorporated herein by reference, discloses one method of head loading and unloading wherein the head suspension assemblies (but not the read/write heads themselves) frictionally contact ramps that lift the head suspension assemblies up off the disk surfaces during shutdown or lower the head suspension assemblies to just above the disk surfaces during startup.
However, loading and unloading of read/write heads using frictional contact, as in the Morehouse et al. patent, has its own share of problems. Upon startup, as the head suspension assemblies slide down and eventually slip off the ramps and onto the disk surfaces, the read/write heads may develop significant pitch and roll (non-parallel orientation with respect to the disk surface), causing edges of the read/write heads to contact disk surfaces despite the presence of an air bearing. In addition, manufacturing and assembly tolerances in the ramps and head suspension assemblies combined with frictional variations due to changing atmospheric conditions may cause the read/write heads to slide down the ramps at an improper loading velocity, resulting in read/write head contact with the disk surfaces. Furthermore, the frictional contact between the head suspension assemblies and the ramps will create, over time, wear debris detrimental to the integrity of the disk surfaces.